MXPA03002996A

MXPA03002996A - Method for reducing the sox emission from a plant for manufacturing cement clinker and such plant.

Info

Publication number: MXPA03002996A
Application number: MXPA03002996A
Authority: MX
Inventors: Jensen Lars Skaarup
Original assignee: Smidth & Co As F L
Priority date: 2000-10-05
Filing date: 2001-09-19
Publication date: 2003-07-14
Also published as: WO2002028512A1; AU2001286169B2; JP2004510677A; US20040040441A1; ES2337023T3; CA2422573C; RU2259226C2; KR100779326B1; BR0114384A; DE60140562D1; JP5118800B2; CZ2003766A3; CA2422573A1; PL202321B1; TW546163B; KR20030059180A; EP1337314A1; CN1466481A; DK1337314T3; BR0114384B1

Abstract

Provided is a method and plant for reducing SO<SUB>2 </SUB>emissions in which a catalyst for catalyzing the formation of cement clinker is extracted from kiln exhaust gas and recycled.

Description

METHOD TO REDUCE SOX EMISSION FROM A PLANT TO MANUFACTURE CEMENT CLINKER AND THIS PLANT Description of the invention. The present invention relates to a method for reducing the S0X emission of a plant for manufacturing cement clinker by means of which the unrefined cement powder is preheated and burned in a plant comprising a cyclonic preheater and a kiln. The invention also relates to a plant for carrying out the method. Plants of the kind mentioned above for making cement clinker are generally known in the literature. The emission of SO2 from such modern kiln plants to make cement clinker is usually relatively low due to the fact that the sulfur contained in the fuel inlet for the kiln and for any kiln is very effectively bonded in the form of sulfate, which is discharged from the oven into the clinker. However, some emission of the preheater may occur if the raw materials you use contain sulfur, as is the case in frequently found minerals such as iron pyrite and marcasite. The reason for this is that the iron pyrite FeS2 is decomposed in the preheater at temperatures of REF: 145789 around 550 ° C according to the equation: (1) FeS2 = FeS + S then, the evaporated S is immediately converted into SO2 when burned. The FeS is somewhat more resistant and reaches the calcination zone before being burned, and the SO2 thus generated is subsequently linked by CaO in a manner similar to that produced from the fuel. This happens according to the reaction equation: (2) S02 + CaO + ½ 02 = CaS04 In the case of an iron pyrite content in the raw materials, there is a risk that approximately half of the sulfur content may escape in the shape of S02. Reducing the degree of any S02 leakage is a known practice for introducing an absorbent in the form of CaO, Ca (0H) 2 or other basic components at some location in the preheater so that So2 can bind in the sulphite form: (3) CaO + S02 = CaS03 In the subsequent process step, the sulphite will be converted to sulfate. A significant advantage of this known method is that it involves the use of an excess amount of absorbent, making the method relatively expensive, particularly if the absorbent being used has to be purchased from an external source.

From the patent O 93/10884 a method is known by which the exhaust waste gases containing CaO loaded powder are extracted from a location close to the calcination furnace and are directed to the location in the preheater where the SO2 absorption. The method works, but requires a very substantial amount of CaO, thus reducing to some degree, the efficiency of the preheater as a heat exchange unit. The Danish patent application No. ?? 1999 00867 provides an improved method whereby non-refined cement powder is extracted, cooled and milled before being introduced into the preheater. However, this method also has the disadvantage of a reduced efficiency of the preheater as a heat exchange unit. The purpose of the present invention is to provide a method, as well as a plant for the manufacture of cement clinker by means of which an economical and effective reduction of the S0X emission is achieved without resulting in a remarkable reduction in the efficiency of the preheater. This is achieved by a method of the kind mentioned in the introduction, and which is characterized by a catalyst in the form of a chloride compound and / or a mixture of several chloride compounds, which has the property that will be present in solid form. or melted in the preheater zone where SO2 is formed, and in this way should be effective, and in evaporated form in the furnace, is introduced into the preheater in its upper cyclonic stage or in the next stage, the catalyst is directed downwards through the preheater to the furnace, a partial amount of the exhaust gas waste stream of the The furnace containing the catalyst in the evaporated form is extracted from the furnace, the extracted exhaust gas gas stream is cooled so that the catalyst is present in solid form, the solid matter is separated from the cooled exhaust gas exhaust stream, and at least some of the solid, separated matter containing the catalyst is recirculated for repeated introduction into the preheater. By means of this act an effective reduction of the S02 emission is obtained. The reason for this is the surprising observation that the chloride compounds and / or a mixture of various chloride compounds having the properties mentioned above with respect to the melting point and boiling point will promote the catalytic reaction according to equation (3). ) CaO + S02 = CaS03 and also promote the reaction: (4) CaC03 + S02 = CaS03 + C02 In this way, it has been proved that it is possible, surprisingly, that the catalytic S02 reacts with calcium carbonate CaC03, which, like this, it constitutes approximately 80% of the raw materials. Since a reagent, specifically CaC03 / is present in great abundance, the reduction of S02 can be effected without the use of some foreign chemical, and, in addition, the reaction, and therefore the reduction of S02, must be assumed to be approximately complete. The plant for carrying out the method according to the invention is characterized in that it comprises a means for introducing a catalyst into the preheater in its upper cyclonic stage or in the next stage as well as a bypass system comprising a means for extracting a partial stream of residual waste gas from the furnace, a means for cooling the extracted exhaust gas waste stream, and a means for separating the solid matter from the cooled waste gas stream and a means for enclosing at least a part of the exhaust stream. of the separated solid matter containing the catalyst for repeated introduction into the preheater. The additional features of the plant will be apparent from the detailed description provided below.

The catalyst must be introduced separately into the preheater. However, it is preferred that the catalyst be mixed with the raw materials, preferably in the raw material grinding plant, to be introduced with it into the preheater together with the raw materials. It is also preferred that the separated solid matter containing the catalyst which is recirculated for repeated introduction, is mixed with the raw materials in the raw material grinding plant. In cases where the amount of recirculated catalyst is insufficient, it will be possible to supplement with new catalyst. Various chloride components such as CaCl 2, KCl, NaCl, MnCl 2 and FeCl 3 can be used as the catalyst. The chloride compounds can be used separately, but in order to obtain a catalyst having suitable properties, particularly with respect to the melting point, it is preferred that a mixture of different chloride compounds be used. Since S02 is formed essentially in the preheater at a temperature above 550 ° C, advantageously the melting point of the catalyst should be less than 550 ° C at a pressure of 1 atmosphere. A variety of existing kiln plants incorporate a diverting system designed to vent the chloride and alkali metals of the kiln system. In such cases, the diversion system will also be used to extract, cool and separate exhaust gases from the kiln, which contain the catalyst. However, in this case the separated solid material will contain constituents such as Cl, Na and K, which may be undesirable elements in the cement, and, therefore, only a portion of this material will be recirculated for repeated introduction into the preheater, and, in addition, this will make it necessary to supplement with new catalyst. The invention will be explained in further detail in the following with reference to the drawing, which is diagrammatic, with its single figure showing a plant for carrying out the method according to the invention. The figure shows a plant for manufacturing cement comprising a cyclonic preheater 1 consisting of cyclones 2, 3 and 4, a calcination furnace 5 with a subsequent separation cycle 6 and a rotary furnace 7. The plant also comprises a clinker cooler 9 for cooling the burnt cement clinker, and a duct 11 for conveying the preheated cooling air to the calcination furnace 5. The raw material of a raw material grinding plant 21 is introduced into a waste gas duct Exhaust 8, which connects the two upper cyclones 2,3 of the preheater and is preheated in counterflow to the residual exhaust gas in its passage through the three cyclones, after being calcined in the calcination furnace 5. From the exit of the At the bottom of the separation cyclone 6, the calcined raw material is directed to the rotary kiln 7. The residual waste gas from the rotary kiln 7 and the calcination furnace 5 is extracted from the kiln. calcination 5 through cyclone 6 and raised through preheater 1 by means of a fan 10. According to the invention, a catalyst is supplied in the form of a chloride compound and / or a mixture of several chloride compounds within of the preheater in its upper cyclone stage or in the next stage, which constitutes the area of the preheater in which the S02 is formed. The catalyst can be supplied separately within the exhaust waste gas line 8 by means of an opening 8a or in the corresponding exhaust waste gas conduit 12 which connects the cyclone 4 with the cyclone 3. However, it is preferred that the catalyst is supplied to the raw material grinding plant 21 in order to obtain an effective mixture with the raw materials and that the catalyst is supplied with which to the preheater by means of the opening 8a intermixed with the raw materials. Subsequently, the catalyst will be taken, together with the raw materials, down through the preheater 1 to the furnace 7. In the preheater, the catalyst will catalyze the absorption of S02 by promoting its reaction with CaO for the formation of CaS03 and also its reaction with CaCCb for the formation of CaSÜ3 and CO2. The CaS03 formed will react additionally to form CaS0, which will be discharged from the kiln in the clinker. Having completed this task in the preheater, the catalyst will end up in the rotary kiln where, due to the prevailing oven temperature of more than 1100 ° C the catalyst will be present in an evaporated form, which is an essential condition to extract the catalyst from the system from the oven. This is done by means of a duct 14 by extracting a partial stream of exhaust gas, which contains the catalyst in evaporated form and powder, and flowing the inlet end of the material of the rotary kiln. The extracted exhaust gas waste stream is then partially cooled by injecting air into the conduit 14 via the air injection means 16 and partially in a conditioning tower 15 subject to the injection of water, so that the catalyst is present. in solid form. The catalyst will be essentially condensed to the powder in the alkaline chloride form during the cooling process. After cooling, the solid matter is separated from the cooled stream of exhaust waste gas in a filter array 17 from which the filtered waste gas exhaust stream, via a fan 18 and a stack 19, is released within the atmosphere, while at least a portion of the filtrate containing the catalyst is recirculated to the raw material grinding plant 21 or alternatively directly to the preheater via an unspecified means of transport for repeated introduction into the preheater. In this document, the raw material grinding plant is shown only as a table, to which is added a variety of the raw material components A, B and C and possibly the catalyzed one.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims

Claims Having described the invention as above, the content of the following claims is claimed as property: 1. A method to reduce the SOx emission of a plant to manufacture cement clinker, by means of which the non-refined cement powder is preheated and burned in a plant comprising a cyclonic preheater and an oven, characterized in that a catalyst in the form of a chloride compound and / or a mixture of several chloride compounds, having the property that will be present in solid or molten form in the area of the preheater where the S02 is formed, and in this way must be effective, and in evaporated form in the furnace, is introduced into the preheater in its upper cyclonic stage or in the next stage, the catalyst is directed down through the preheater to the kiln, a partial amount of the exhaust gas stream from the kiln that contains the catalyst in the evaporated form is extra From the furnace, - the exhaust gas extracted stream is cooled so that the catalyst is present in solid form, - the solid matter is separated from the cooled waste gas stream of exhaust, and at least some of the material solid, separated containing catalyst is recirculated for repeated introduction into the preheater.
2. A method according to claim 1, characterized in that the catalyst is introduced separately into the preheater.
3. A method according to claim 1, characterized in that the catalyst is mixed with the raw materials, preferably in the mill of raw materials and is introduced into the preheater mixed with the raw materials.
4. A method according to claim 1, characterized in that the solid, separate material containing the catalyst, which is recirculated for repeated introduction, is mixed with the raw materials in the raw material grinding plant.
5. A method according to claim 4, characterized in that the new catalyst is complemented.
6. A method according to claim 1, characterized in that the catalyst comprises one or more chloride compounds such as CaCl2, KCl, NaCl, MnCl2 and FeCl3.
7. A method according to claim 6, characterized in that the catalyst has its melting point lower than 550 ° C at a pressure of 1 atmosphere. A plant for carrying out the method according to claim 1, comprising a cyclonic preheater and an oven, characterized in that it comprises a means for introducing a catalyst into the preheater in its upper cyclonic stage or in the next stage as well as also a bypass system comprising a means for extracting a partial stream of exhaust gas from the furnace, a means for cooling the extracted exhaust gas stream, a means for separating the solid matter from the cooled stream of waste gas and a means for recirculating at least a part of the separated solid matter containing the catalyst for repeated introduction into the preheater. Summary of the Invention A description of a method as well as a plant for reducing the S0X emission of a plant for manufacturing cement clinker is provided by which the non-refined cement powder is preheated and burned in a plant comprising a preheater cyclonic (1) and an oven (7). The method is characterized in that a catalyst in the form of a chloride compound and / or a mixture of several chloride compounds is introduced into the preheater (1) in its upper cyclonic stage or in the next step (2,3), the catalyst is directed downwards through the preheater (1) to the furnace (7), a partial amount of the exhaust gas waste stream from the furnace containing the catalyst in evaporated form is removed from the furnace (7), the extracted exhaust gas gas stream is cooled so that the catalyst is present in solid form, the solid matter is separated from the cooled stream of exhaust waste gas and at least some of the separated solid matter containing the catalyst is recirculated for repeated introduction into the preheater (1). With which an effective reduction of the emission of S02 is obtained. The reason for this is that the chloride compounds and / or a mixture of various chloride compounds will promote the catalytic reaction of S02 with CaO for the formation of CaSÜ3 and further promote the reaction of S02 with CaC03 for the formation of CaSÜ3 and C02. Since CaCO3 is present in great abundance, the reduction of S02 can be made without the use of some foreign chemical.